1. Field of the Invention
This invention is in the field of medicinal chemistry. In particular, the invention relates to small molecules which function as antagonists of the interaction between p53 and MDM2 and their use as a new class of therapeutics for the treatment of cancer and other diseases.
2. Related Art
The aggressive cancer cell phenotype is the result of a variety of genetic and epigenetic alterations leading to deregulation of intracellular signaling pathways (Ponder, Nature 411:336 (2001)). The commonality for all cancer cells, however, is their failure to execute an apoptotic program, and lack of appropriate apoptosis due to defects in the normal apoptosis machinery is a hallmark of cancer (Lowe et al., Carcinogenesis 21:485 (2000)). The inability of cancer cells to execute an apoptotic program due to defects in the normal apoptotic machinery is thus often associated with an increase in resistance to chemotherapy, radiation, or immunotherapy-induced apoptosis. Primary or acquired resistance of human cancer of different origins to current treatment protocols due to apoptosis defects is a major problem in current cancer therapy (Lowe et al., Carcinogenesis 21:485 (2000); Nicholson, Nature 407:810 (2000)). Accordingly, current and future efforts towards designing and developing new molecular target-specific anticancer therapies to improve survival and quality of life of cancer patients must include strategies that specifically target cancer cell resistance to apoptosis. In this regard, targeting crucial negative regulators that play a central role in directly inhibiting apoptosis in cancer cells represents a highly promising therapeutic strategy for new anticancer drug design.
The p53 tumor suppressor plays a central role in controlling cell cycle progression and apoptosis (Vogelstein et al., Nature 408:307 (2000)). It is an attractive therapeutic target for anticancer drug design because its tumor suppressor activity can be stimulated to eradicate tumor cells (Vogelstein et al., Nature 408:307 (2000); Chene, Nat. Rev. Cancer 3:102 (2003)). A new approach to stimulating the activity of p53 is through inhibition of its interaction with the protein MDM2 using non-peptide small molecule inhibitors (Chene, Nat. Rev. Cancer 3:102 (2003); Vassilev et al., Science 303:844 (2004)). MDM2 and p53 are part of an auto-regulatory feed-back loop (Wu et al., Genes Dev. 7:1126 (1993)). MDM2 is transcriptionally activated by p53 and MDM2, in turn, inhibits p53 activity by at least three mechanisms (Wu et al., Genes Dev. 7:1126 (1993). First, MDM2 protein directly binds to the p53 transactivation domain and thereby inhibits p53-mediated transactivation. Second, MDM2 protein contains a nuclear export signal sequence, and upon binding to p53, induces the nuclear export of p53, preventing p53 from binding to the targeted DNAs. Third, MDM2 protein is an E3 ubiquitin ligase and upon binding to p53 is able to promote p53 degradation. Hence, by functioning as a potent endogenous cellular inhibitor of p53 activity, MDM2 effectively inhibits p53-mediated apoptosis, cell cycle arrest and DNA repair. Therefore, small-molecule inhibitors that bind to MDM2 and block the interaction between MDM2 and p53 can promote the activity of p53 in cells with a functional p53 and stimulate p53-mediated cellular effects such as cell cycle arrest, apoptosis, or DNA repair (Chene, Nat. Rev. Cancer 3:102 (2003); Vassilev et al., Science 303:844 (2004))
Although high-affinity peptide-based inhibitors have been successfully designed in the past (Garcia-Echeverria et al., Med. Chem. 43:3205 (2000)), these inhibitors are not drug-like molecules because of their poor cell permeability and in vivo bioavailability. Despite intensive efforts by the pharmaceutical industry, high throughput screening strategies have had very limited success in identifying potent, non-peptide small molecule inhibitors. Accordingly, there is a need for non-peptide, drug-like, small molecule inhibitors of the p53-MDM2 interaction.
The design of non-peptide small-molecule inhibitors that target the p53-MDM2 interaction is currently being pursued as an attractive strategy for anti-cancer drug design (Chene, Nat. Rev. Cancer 3:102 (2003); Vassilev et al., Science 303:844 (2004)). The structural basis of this interaction has been established by x-ray crystallography (Kussie et al., Science 274:948 (1996)). The crystal structure shows that the interaction between p53 and MDM2 is primarily mediated by three hydrophobic residues (Phe19, Trp23 and Leu26) from p53 and a small, deep hydrophobic cleft in MDM2. This hydrophobic cleft is an ideal site for designing small-molecule inhibitors that can disrupt the p53-MDM2 interaction (Chene, Nat. Rev. Cancer 3:102 (2003)).